Gas-operated automatic firearm with forwardly moving barrel



w. A. scHAlcH 2,628,536 GAS-OPERATED AUTOMATIC FIREIARM WITH FORWARDLY MOVING BARREL Feb. 17, 1953 l1 Sheets-Sheet 1 Filed Oct. lO, 1945 l N? .ma full 6 3 5, 8 2 6, 2 M E RR Hmm mmm AAM W U Y im Amm w Feb. 17, 1953 GAS-OPERAT WITH FoRw 1l Sheets-Sheet 2 Filed Oct. l0, 1945 GMW v LEE.

W. ERAT Feb. 17, 1953 A. SCHAICH GAS-OP ED AUTOMATIC FIREARM WITH FORWARDLY MOVING BARREL 1l Sheets-Sheet 3 Filed Oct. 10, 1945 hmmm,

hws/wrm A-LLEUR A 5 r11-IAT. L11-1 @2M gf/ @mf-ff (@JMM @MQW-3 Feb. 17, 1953 w. A. scHAxcH 2,628,536 GAS-OPERATED AUTOMATIC FIREARM WITH FORWARDLY MOVING BARREL Filed oct. 1o, 1945 11 sheets-sheet 4 CU .y l I l m @141 W/ fmM/wmw @www Feb. 17, 1953 w. A. scHAlcH 2,628,536

GAS-OPERATED AUTOMATIC FIREARM WITH FORWARDLY MOVING BARREL Filed Oct. l0, 1945 ll Sheets-Sheet 5 im I! lmmmxm.

Feb. 17, 1953 w. A, scHAlcl-l 2,628,535

GAS-OPERATED AUTOMATIC F'IRERMi WITH FORWARDLY MOVING BARREL Filed oct. 1o, 1945 11 sheets-sheet e wumn/bofv A/'ILEJUE ALE EHAI CLI-1,

SHV/nalga W. A. scHAlcH 2,628,536 ERAT oMATIc FIREARM FoRwAR MOVING BARREL ED AUT DLY GAS-OP WITH Feb. 17, 1953 ll Sheets-Sheet 7 Filed Oct. 10, 1945 WI LEUR A5 @HAI IBI-I,

Feb. 17, 1953 W, A SCHAlCH 2,628,536

GAS-OPERATED AUTOMATIC FIREARM WITH FORWARDLY MOVING BARREL Filed Oct. lO, 1945 l1 Sheets-Sheet 8 WILEUR AU @HAI [1I-I,

Feb. 17

w. A. scHAlcH GAS-OPERATED AUTOMATIC FIREARM WITH`FORWARDLY MOVING BARREL Filed Oct. l0, 1945 n Ir ll Sheets .sheet 9 ML'UE Lul-IAIBH W. A. SCHAICH GAS-OPERATED AUTOMATIC F'IREARM Feb. 17, 1953 l1 '.Sheets-Sheefl 10 Filed 001'.. 10, 1945 grime/w90@ @lum/MW@ a WILBU A mI-IAI x11-1,

@M .ffy @Off/#fw w. A scHAlcH 2,628,536 GASOPERATED AUTOMATIC FIREARM WITH FORWARDLY MOVING BARREL ll Sheets-Sheet 1l V/L .ua 7/ @doamp WILEUR 11i-:A1 QH,

Feb. 17, 1953 Filed oct. 10, 1945 Patented Feb. 17, 1953 UNITED STATES OFFICE GAs-'oPERA'rEii AUTOMATIC FIREARM WITH FORWARDLY MOVING BARREL (Granted under 'rit-ie 35, s. code (1952),

sec. 266) 45 Claims;

arranged to move forwardly with respect to xed breech elements have long been known in `the art. An action of this type has also been applied to an automatic rearm for a low-powered cartridge, such for example. the type fired in pistols,

as evidenced by the disclosure of U. S. Patent No.

1,376,456, issued May 3, 1921, to Moore. Heretofore, however', there apparently has been no successful application of the forward moving barrel action to an automatic firearm designed for a high-powered cartridge, such for example,

as U. S. Army', caliber .30, M1906'. l

It has been discovered by the inventor of this' application that an action based upon a forward moving barrel can be expeditiously applied to an automatic firearm designed to fire a high-powered cartridge, providing a firearm structure of utmost simplicity and improved safety in per-v formance. The improved results obtained by such construction are, in a large measure, based upon discovery of a fundamental principle appli- .l

cable only to a firearm action having a xed breech and a forwardly moving barrel and which does not apply to conventional type firearms where the breech member is movable with respect to the barrel.

This principle, which heretofore has apparently been unappreciated, has been thoroughly demonstrated and proved by experiment. Concisely stated, it has been discovered that the resultant force developed on the barrel by the firing of a cartridge therein, when the barrel is considered independently ofthe breech mechanism, is a force acting in a forward direction and such force is substantially less than, and, in fact, only a fraction of the rearward force exerted on the breech mechanism through the base of the cartridge.

Thus, if the locking mechanism ot the automatic firearm action is designed to resist the forward force on the barrel rather than the rearward force on the bolt, then the strength required for such locking mechanism is substantially reduced.

It has been heretofore believed necessary that the locking rncchaiiisn'i4 which normally resists rearward movement of the bolt be located as near as possible to the face of such bolt to eliminate increase of headspace caused by stretch of the metal parts disposed between the bolt face and the point of locking due to the very large rearward force set up by the iring of a cartridge. In accordance with this invention, the locking mechanism may be located out on the barrel and well forward of the chamber. Thus the locking mechanism may -be located immediately adjacent a gas port in the barrel and, hence, there is no necessity for the long operating rod found in conventional actions running between the gas system on the barrel and the movable breech member. Consequently, simplicity of structure is obtained by the application of this invention. In addition, since the entire inertia mass of the barrel opposes the opening of the breech, an unlocking mechanism incorporating little or no dwell time may be utilized with safety, so long as the gas port in the barrel actuating the unlocking mechanism is located forwardly of the barrel region wherein maximum gas pressure occurs.

Another long recognized defect of conventional automatic weapons, and particularly the gas operated, movable bolt type weapons, is that the cyclic rate of such weapons is excessively high. Such high cyclic rate when firing full automatic greatly disturbs the accuracy of iiring and produces extreme rapid heating of the barrel, thereby eiectively limiting the length of burst that may be fired to 200 rounds or less. Even when conventional weapons were fired semi-automatically, an inherent high cyclic rate produced eX- treme acceleration of the moving parts of the mechanism (particularly the operating rod and the bolt) and high impact forces resulted when the mechanism reached the ends of its stroke.

In accordance with this invention, the barrel constitutes the major moving element of the mechanism. Obviously the weight of the barrel is many times that of the bolt of a conventional rearm. Since the cyclic rate of a gas operated automatic firearm is primarily dependent upon the mass of moving parts, it is readily apparent that an automatic rearm constructed according to this invention will have a cyclic rate which is substantially below that of a conventionally designed Vgas-oygxerated iirearm, hence reducing the impact stresses on all parts and making the gun more readily controllable in full automatic lire. A further advantage of the structure achieved by the application of this invention `is that its simplicity would permit a substantial over-all reduction in weight of the firearm if the barrel mass was selected substantially the same as the conventional firearm. It is, therefore, possible by the application of this invention to utilize a heavier barrel with-out increasing the weight of the weapon over that of conventionally designed firearms. Accordingly, the cyclic rate of the improved firearm i-s still further decreased and t-he heat cap-acity of the barrel increased. Both of these factors are particularly important in weapons designed for military purposes.

in addition, in the lpreferred embodiments of this invention substantially 75 percent or more of the entire mass of the firearm is disposed in surrounding, and hence in good heat conducting relation to the barrel, thu-s further increasing the heat dissipating ability of the barrel.

Accordingly it is an object of this invention to provide an improved automatic firearm composed of simple, readily manufacturable parts and providing reliable operation, long endurance life, and compl-ete safety of operation.

Another object of this invention is to provide an improved firearm of the automatic type w-herein the breech member is fixed and the barrel moves forwardly with respect thereto.

A particular object of this invention is to provide an improved gas operated automatic rearm having a barrel movable forwardly with respect to the breech wherein the locking mechanism between the breech and barrel is located at an intermediate point on the barrel and immediately r" adjacent the gas port in the barrel.

A further object of this invention is to provide `an improved automatic rearm structure whcrein the barrel moves forwardly with respect to a xed breech member and the residual gas pressure operates .directly on the barrel t-o assist in such forward movement.

A further object of this invention is to provide an automatic firearm construction wherein the barrel moves forwardly with respect to the breech and the need for any locking mechanism is eliminated by proper proportioning of the mass of the barrel and associated components.

A further object of this invention is to provide an improved automatic firearm construct-ion, characterized 4by the simplicity and small number of its components, which is susceptible of large quantity economical manu-facture inasmuch as practically all components are of cylindrical configuration or can be produced by stamping operations.

As heretofore state-d, this invention is based upon the discovery that the locking force required to lock a forwardly movable barrel to a xed breech when firing a high-powered cartridge was much less than the force required to lock a conventional action utilizing a rearwardly movable bolt locked to a xed or rearwardly movable barrel. The small magnitude of the lforces required to lock a forwardly movable barrel to a fixed-breech may be readily determined by analysis. Considering first a barrel chambered to fire a straight case, it is readily apparent that when the :barrel is considered as an element separate from the breech member that the only forces operative thereon are the following:

1. A forward force on the barrel exerted by the projectile during its initial movement when it is being engraved by the lands of the rifling of the barrel. This force exists generally for a period on the order of a ten-thousandth of a second duration.

2. A forward force on the barrel produced by the frictional drag of the projectile on the barrel. It is `deemed obvious that this force is of a very 4 small magnitude once the engraving is accomplished, although it exists for the entire time that the projectile is in the barrel.

3. A forward force on the barrel represented by the forward component of the reaction force produced between the helical-shaped lands and the projectile. This force may be readily calculated for any particular cartridge and barrel knowing the muzzle velocity of the projectile, the barrel time of the projectile and the twist of the riling.

4. A rearward force on the lbarre-l produced by the reaction of the gases issuing from the muzzle upon the barrel.

When a .so-called bottle-neck cartridge cas-e is utilized, which is the construction commonly 'found in high-powered cartridges, such, for example, as the U. S. Army cal. .30, M1905, then an additional component of force is produced on the barrel. This force is produced by the action of the gas pressure within the barrel upon the resultant rearwardly facing area of the cartridge case. This area generally comprises the difference in interior area of the base of the cartridge land the maximum cross-sectional area of the projectile.

Adding all of the described forward forces together, the res-ult for any commonly known cartridge and barrel is a res-ultant forward force on the barrel which is 25 to '75 percent less than the rearward force exerted by the same cartridge upon the breech member.

It has already been menti-cned that a firearm action built around a forwardly movable barrel results in a simplified design and hence an appreciable saving in weight of the complete firearm.' In accordance with this invention a much greater percentage of the mass of the gun may lbe incorporated on the barrel. This will be recognized to those skilled in the art as a most Idesirable condition inasm-uch as the mass of the barrel is really the most es-sential mass of the gun. The heavier the barrel, obviously the greater is its ability to absorb heat pro-duced by firing. However, in the application of this invention, the increase in mass of the barrel has the additional advantage of decreasing the size of th-e locking element. The barrel mass, in a sense,

constitutes the blow-back mass of the gun.v

Thus for any medium-powered cartridge, for example, the U. S. Carbine cal. .30, M1, an action constructed in accordance with this invention, yutilizing a forwardly movable `barrel with as much mass built into the barrel Aas consistent with the overall weight requirements of the weapon, requires no locking system at all, or at the most, merely a non-positive, `delay lock. The reduction in the force operating to separate the barrel from the breech, coupled with the large mass of the barrel resisting acceleration of the barrel by such forces, insures that the barrel will not move substantiallyv away from the breech until the pressure Within the barrel has dropped to a safe value.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

Fig. l is a longitudinal sectional View of the rear portion of an automatic firearm embodying this invention. The firearm is shown with the hammer mechanism in its red position and the barrel in battery position.

aeasse Fig. 2 is a top elevational view of the unlocking ring utilized in the firearm construction of Fig. 1.

Fig. 3 is a longitudinal sectional view of the front portion of the firearm shown in Fig. l.

Fig. 4 is an enlarged sectional view of Fig. 3 taken on the plane 4 4 and showing the locking elements in their battery positions.

Fig. 5 is a view similar to Fig. 4 but showing the locking elements in their manually unlocked position.

Fig. 6 is a longitudinal sectional view of the forward end of a firearm similar to that shown in Fig. 1, showing an alternative jet action type of locking mechanism.

Fig. 7 is a sectional view taken on the. plane 1-1 of Fig. 6.

Fig. 8 is a longitudinal sectional view of the forward end of a rearin similar to vthat shown in Fig. 1, showing an alternative roller type of locking mechanism.

Fig. 9 is a view similar to Fig. 8 but showing the elements in their counter-battery positions.

Fig. 10 is a partial sectional view of Fig. 8 taken along the plane l il-HL Fig. l1 is an enlarged scale longitudinal sectional view of the breech portion of a firearm embodying a second modification of this invention shown with the elements thereof in their battery positions.

Fig. 12 is a continuation of Fig. 1l showing the forward end of the barrel.

Fig. 13 is a view similar to Fig. 1l but showing the elements of the firearm in their counterbattery position.

Fig. 14 is an enlarged sectional View of Fig. 13 taken along the plane Ill-Hl thereof. For clarity, the magazine and cartridges have not been shown in this view.

Fig. 15 is a side elevational view of the tube or receiver utilized in the rearm of Fig. 11.

Fig. 16 is a continuation of Fig. 15 showing the forward end of the tube.

Fig. 17 is a fragmentary sectional view of the breech block showing the retaining washer for the firing pin.

Fig. 18 is an elevational view of the locking element utilized in the firearm of Fig. 11.

Fig. 19 is a sectional view taken along 'the plane l 9-1 9 of Fig. 11.

Fig. 20 is an elevational assembly view of an automatic firearm vembodying a third modification of this invention.

Fig. 21 is also an enlarged scale, longitudinal, sectional View of the firearm of Fig. 20 showing the forward portion of the firearm mechanism.

Fig. 22 is a sectional view taken along the plane 252-22 of Fig. 2l.

Fig. 23 is a sectional view taken along the plane 23-23 of Fig. 21.

Fig. 24 is an enlarged scale, elevational view lof 'the operating sleeve utilized in the rearm of Fig. l2l).

Fig. 25 is an enlarged scale, elevational view of the locking element utilized in the firearm of Fig. 20.

Fig. 26 is a horizontal, sectional view of the breech portion of an automatic firearm embodying a modification of this invention, characterized `by the elimination of any locking elements.

Fig, 27 comprises essentially a forward eXtension'of the View of Fig. 26.

Referring to the drawings a number of specific applications of this invention will be described `but it should be understood that the novel design principles incorporated therein are equally applicable to any type of automatic firearm and 6 may be applied to produce an improved automatic rearm action for any cartridge.

Gas operated, positive lock, automatic rifle Referring to Figs. 1-5 there is shown an automatic rifle embodying this invention comprising a stock l, a xed breech member l mounted in said stock, a hollow guide member or tube 20 secured at its rear end to the breech member I0, a barrel 3u reciprocatingly mounted within tube 20 for forward movement with respect to breech block IG, a locking unit li (Fig. 3) constructed to lock the barrel to the breech in battery position thereof and to unlock the barrel -responsive to the gas plessure developed therein by thedischarge of a cartridge, a gas actuating mechanism 5B constructed to move the barrel forwardly after it has been unlocked from the breech, a hammer and trigger mechanism Si! for firing a cartridge chambered in the barrel 30, and a magazine 10 for supplying successive cartridges to the action.

Breech block I0 is provided with a forwardly opening, cup-shaped, threaded recess I! in the forward portion thereof into which the end of tube 2Q is threadably secured. The cooperating threads between tube 20 and recess i l are preferably of the interrupted type, permitting tube 20 to be assembled to breech block l0 by a rotation of degrees or less.

The central portion of the base of recess Il is countersunk to form a cartridge seating recess l2. An axial opening I3 is provided through breech block lf3, opening in the center of the cartridge seating recess i2 and shaped to accommodate a firing pin |00. Firing pin opening I3 is counterbored at its rear portion, indicated at le, to accommodate an enlarged head portion IGI of firing pin Il. A retracting spring 192 surrounds the body portion of firing pin Illi and seats between the base of the counterbore I4, and the head liii of the ring pin. Firing pin Iii@ is retained within breech block I9 by means of a pin HQ which passes transversely through a slot H2 provided on the exterior of firing pin (06.

A longitudinally extending slot Il is provided in the bottom portion of breech block l0 to house a trigger 6l? and magazine latch '16. Breech block l@ is also provided with an integral, forwardly projecting portion I3 which defines a .rectangular opening through which magazine 10 may be inserted.

The receiver or tube 2G, which acts as a guide for the reciprocal movement of barrel 38, extends forwardly from the breech block I0 to a distance preferably not less than one-third of the length of barrel 3S. rlhe tube 29 defines a rear uniform large diameter cylindrical bore Zilli in which the rear large diameter portion 300 of 'barrel Sil slides in bearing relation. A magazine slot 2l is provided in the bottom of the tube to receive a magazine lll. The forward portion 2li) (Fig. 3) of tube 2Q has somewhat thicker walls and defines a cylindrical bore 25| of smaller diameter than the bore portion 2530 but concentric therewith, and a forward reduced diameter portion 38| of the barrel cooperates with portion 20l of the tube in bearing relation. An annular buffer 22 is provided sliding freely around barrel portion 3?! and within tube portion 205. A shoulder 33 is defined at the juncture of the two diameter portions Sfiil and Sill of the barrel. A spring retainer 2&3 is provided comprising an annular member which surrounds barrel portion Se! and abuts against barrel shoulder 393. A pair of integral radial projections 2534i are provided on spring retainer Zei! in dianietric relablock l0.

tionship which project out through a pair of longitudinal slots 205 provided in tube 20 in opposed relationship. The width of the slots 205 is suitably proportioned with respect to the spring retainer i203 so that spring retainer 203 may be inserted in its iiat position into the interior oi tube 20 through the slots 205 and then rotated 90 degrees to bring it into its operative position.

An operating spring 20e surrounds tube 20 and operates between an integral shoulder 20 on the forward end of tube 2d and the projections 204 of spring retainer 203. It will be obvious that spring 206 thus biases the barrel rearwardly to its battery position with respect to the breech The forward stroke of the barrel is limited by engagement of spring retainer 203 with buiier 202 when the buiter 2532 is abutting the interior shoulder 2% formed at the juncture o interior diameter portions 20) and 20| of the tube. It should be noted that the exterior shoulder 20? on the tube is located suciently forward of the extreme forward position of spring retainer 203 to provide adequate space for the compressed operating spring 205.

As has heretofore been stated, one of the principal advantages of the application of this invention is that the locking forces are so reduced that the locking elements may be locked at a point out on the barrel immediately adjacent the gas port.

In Figs. 3, 4.1, and there is disclosed one form of locking mechanism while in Figs. 6, 8, 11, and 2l, alternative forms are disclosed. Each form of locking mechanism however orers similar advantages of simplicity of structure, and reliability and safety of performance and is particularly effective with the forward moving barrel construction inasmuch as the mechanism can be located on the barrel in the vicinity of the gas port.

The locking mechanism 40 shown in Figs. 3 5 comprises a plurality of piston plugs i630 which are mounted in radially arranged holes 209 provided in the forward thick walled portion 2li! oi tube 20. In view of the fact that the steel generally utilized in firearm barrels is in a relatively soft condition and would deiorm when resisting locking forces, a locking ring .fi-@i of hardened steel is pressed onto barrel Locking ring 43! has the samefexterior diameter as barrel portion Ztl and is pressed over a forward reduced diameter end portion 30d of the barrel. Suitable radial holes 402 are provided in locking ring 458i to snugly receive the ends of piston plugs Gili). It will be apparent that when piston plugs l'll are seated in holes 402, the barrel 30 will be rigidl37 locked to the tube and hence to breech block i0. As heretofore mentioned, the locking force which the locking mechanism l0 is required to resist is so substantially reduced by the arrangement of this invention, that the tube 2Q may be formed from relatively thin walled material and yet the stretch of the material lying between the point of locking and the face of the breech block will not detrimentally aiect the saiety of the action. Piston plugs fifi@ are biased toward their locking positions by means of an annular leaf type spring 403 which lies in a slot :105 provided in the outer ends of each of the piston plugs 400.

A plurality of gas ports 4% are provided in barrel running radially from the center of each hole 402 in barrel locking ring @Si into the bore 3l of the barrel. Thus when a cartridge is red and the projectile moves along the bore lll past gas ports 406, a portion of the gases will be diverted through ports 406 and will operate on the base of piston plugs 400, driving such plugs outwardly against the bias of spring 403 and hence unlocking the barrel from the breech. To reduce the gas leakage past piston plugs m0, an annular gasgroove 40% may be provided on each piston plug.

In order that the action may be unlocked y manually at any time, an unlocking ring 401 is provided which surrounds portion 2E0 of tube 20, abutting shoulder 201. A pair of opposed flats 409 are provided in the middle of each of the piston plugs 400. Unlocking ring 40T (Fig. 2) is provided with a plurality of radial holes M0 of diameter proportioned to freely accommodate the end portion respectively of each of piston plugs 300. Peripheral cam slots 4H are provided in unlocking ring 401 communicating with each of the holes M0. On each side wall of each cam slot 4H there is provided inwardly projecting cam ribs iii/ZI. The space between such cam ribs M2 will accommodate the flat portions 409 of the piston plugs 000. The cam ribs M2 are so arranged that by rotation of unlocking ring 401 with respect to tube 20 in a counterclockwise direction as viewed in Figs. 4 and 5, the cam ribs 4l? will engage the outer shoulder formed by flats 400 on piston plugs 400 and cam each of such plugs outwardly to an unlocked position as shown in Fig. 5. Unlocking ring 407 is constructed to be rotated by movement of the handguard of the gun as will be later described.

The end of forward portion 2l@ of tube 20 is constructed to serve as a xed piston member of the gas actuating mechanism 50. Gas actuating mechanism 50 comprises an annular gas cylinder 500 which is threadably secured to the forward portion 304 of the barrel and which denes a rearwardly opening, cup-shaped recess 5e! constructed to slide in bearing relation on forward portion 210 of tube 20. To reduce gas leakage between these cooperating members, a plurality of gas grooves 502 may be provided in both the interior peripheral surface of recess 50| and the exterior of tube portion 2l0. Operating gases are supplied to the above described piston and cylinder arrangement by means of longitudinal grooves M3 provided in locking ring 40i immediately adjacent each of the lock holes 402. With this construction, it is obvious that no gas is supplied to the piston and cylinder arrangement until after the piston plugs are forced out of their locked position. The gases supplied to the gas actuating member 50 will then drive the gas cylinder 500 forwardly and hence carry the barrel 30 forwardly. The gas ports 405 and the gas grooves 4&3 are soA proportioned as to provide suicient gas to rapidly accelerate barrel 30 so that by the time gas cylinder 560 passes off the forward end of tube 20, the

barrel will have sufiicient momentum to complete its forward travel, compressing operating spring 200. However, the maximum velocity achieved by the barrel is substantially less than that required in conventional, movable bolt actions.

As has been previously mentioned, the magazine 'F0 is supported within the forwardly projecting portion I0 of breech block l0 and projects into the interior of tube 20 through slot 2l. Magazine 'IG comprises a sheet metal box having a conventionally arranged follower 'li and spring l2 therein and is constructed to support a double row stack of necked-down cartridges. The top portion and lips of magazine 'I0 (not shown) are, however, constructed in an entirely unique manner producing very desirable feeding conditions when utilized in conjunction with a forwardly moving barrel action. To facilitate the feeding operation, an integral ramp 32 is provided on the breech end of barrel 30. The base of the recess H of breech block I is cut away to provide a suitable recess I9 to accomodate the barrel ramp 32 in the battery position. The function of magazine 1I) is to support the top cartridge in such position that barrel ramp 32 will pass under and engage the nose of such top cartridge. Accordingly, the forward wall of magazine 10 is provided with a cut-away portion (not shown) at the top of its forward wall to permit entry of the barrel ramp 32 under the nose of the top cartridge.

Magazine 'iii is retained in position with respect to breech block l0 by means of magazine latch i6 which lies within the longitudinal slot I'I in breech block Ill. Latch 'I6 is pivotally mounted by engagement of a fixed pin 11 in a slot-like hole 78 in the magazine latch 16. In the rearwardly extending portion of magazine latch 16, there is provided a spring seat recess 19. Trigger BI'I is pivotally mounted at its forward end in the slot I'I in breech block I0 by a transverse pin BIB. A portion 6I9 of the trigger 1 extends forwardly beyond pin SIS and is provided with a spring-seat recess 620. A spring BZI is mounted between the spring-seat 62B in trigger 6 I 'I and the spring-seat recess 'I9 in magazine latch 16. An integral depending projection 83 is provided on magazine latch 16 which projects out of the breech block I0 in position to be engaged by the linger of the operator to permit release of the magazine. A latch portion 84 of magazine latch 16 engages in a suitable notch 85 on the side of magazine l0. The latch portion 84 is so shaped that when a magazine is being inserted into the magazine recess, the magazine latch 'IS will be cammed rearwardly out of the path of the magazine until the notch 85 is aligned therewith.

rhe hammer mechanism for a firearm utilizing a forwardly moving barrel is substantially different from that of a conventional rearm. In the conventional iirearm, the hammer is cocked by being over-ridden by the bolt in its rearward movement. In a firearm constructed in accordance with this invention, the only major moving element is the barrel and that is moving away from the rear of the breech block which is the necessary location of the hammer mechanism. In Fig. 1 a hammer mechanism 60 is shown which accomplishes its cooking during the return rearward movement of the barrel to battery position. This mechanism does not require much space rearwardly of the breech block and hence is particularly adaptable to a dropped stock construction.

To communicate the barrel movement to the hammer mechanism SEI, a cooking rod E3B is provided, the forward end of which is threadably secured in the barrel. Hence Cooking rod 605 serves to maintain the barrel at all times in xed position with respect to the breech block I.

The stock l is conventionally formed and is suitably recessed to accommodate breech block I S, tube and hammer mechanism 6D. The stock i preferably extends forwardly of the magazine support portion i8 of breech block I0, as indicated at 3. A trigger guard and floor plate I may 10 be secured to stock i in any desired manner, such as by anchoring the rear end thereof in the wood of the stock and securing the forward end by a pair of screws 3 extending through the Wood of the stock and threading into the bottom of breech block I.

A wood or plastic handguard 3 (Fig. 3) is provided to cover that portion of the mechanism lying between the forward portion 2 of the stock and gas cylinder 80. A stock mounting ring 4 is provided surrounding tube 29 and secured thereto by a removable pin 22, and is engaged by both the forward portion 2 of the stock and the rear portion of the handguard 3. A conventional, screw tightened stock ferrule 5 is provided, surrounding the forward portion 2 of the stock I and securing it to mounting ring 4.

Handguard 3 essentially comprises a hollow cylindrical member and is arranged to slide in bearing relation with respect to the peripheries of mounting ring 4, unlocking ring 43T, tube shoulder 2li?, and the rear portion of gas cylinder EES. To eliminate excessive wear on the wood or plastic material of the handguard, a plurality of spaced, longitudinal metallic strips 5 are secured to the interior of handguard 3. Suitable notches Mft (Figs. 4 and 5) to accommodate strips 6 are provided in the periphery of unlocking ring 101. Thus rotation of handguard 3 will rotate unlocking ring 4ST. Accordingly, unlocking of the action at any time is accomplished in a convenient manner by limited rotation of handguard 3. The forward end of handguard 3 abuts against an integral shoulder 50A provided on gas cylinder Etc. Thus forward movement of handguard 3 will be imparted to the gas cylinder 500 and thus to the barrel 30. The action may therefore be manually functioned by a slight rotation of handguard 3 followed by a forward thrust of the handguard similar to the movement of pump action guns. This is particularly desirable in that the operator does not have to utilize his trigger hand nor take his eyes off the target.

In military riiles it is common practice to provide an adapter which fits over the muzzle end of the rifle to permit the launching of an explosive grenade therefrom by the action of highpressure gases developed by the ring of a blank cartridge within the barrel. Grenade launching constitutes a severe problem for gas operated rearms inasmuch as the gas pressure at the gas port is not only generally higher than the normal gas pressure but it exists for a substantially longer period due to the time required to accelcrate the substantial mass of the grenade. Under such conditions the gas actuating mechanism receives an excess of power which would cause it to open the action either too soon or too violently, in either case with resultant damage to the rearm.

To permit grenades to be launched from a lirearm of the type described, internal, peripherally extending, slot-like recesses H5 are provided on the inside of unlocking ring 497 adjacent each of the radial holes fl but on the opposite side of such holes with respect to the cam slots 4I I. Recesses H5- are so shaped with respect to the heads of the piston plugs @im that rotation of the unlocking ring it? by handguard 3 will bring the base GI@ of recesses i5 directly over the top of each piston plug Se when such plugs are in locked position. Thus the action is locked in its battery position and c-annot be unlocked by the gas pressure developed within the barrel. Accordingly when it is desired to launch grenades il from this improved ride, a suitable grenade launching attachment (not shown) is secured to the muzzle end or the barrel and a grenade mounted thereon. The grenade launching blank cartridge is loaded into the barrel and the barrel l returned to its battery position. Then the handguard il is rotated. to bring the locking ring to the foregoing described grenade firing position wherein the piston plugs are locked against radial movement. Accordingly, the gas pressure developed in the launching of the grenade cannot achieve the unlocking of the action and hence the possibility of damage to the action is eliminated.

Any desired system of front and rear sights may be applied to this rifle. A conventional form of a rockover rear sight E16 is shown mounted in a dovetailed slot 1171 provided in the top rear portion of breech block 10. A front sight 9!) is removably secured to the muzzle end of barrel 30.

The only requirement for such front sight is that i.

it be readily removable to permit disassembly of v the rifie, and that in reassembly the sight assumes movable key el which is driven by a screw 92 into a key slot 33 provided. in barrel The details of such sight however form no part of this invention.

Disassembly of this improved rifle may be readily accomplished without special tools or equipment. The disassembly steps are as follows:

Magazine l@ is removed by raising the depending projection 33 of magazine l-atch lt; stock ferrule is loosened and slipped off the forward portion 2 of the stock 1. The trigger guard screws 5 are removed and trigger guard 'l is taken olf. The rest of the action may then be freely removed from the stock 1. All elements assembled to the tube 2Q may then be removed from the breech block by slight rotation of the tube 29 with respect to breech block, disengaging the interrupted threaded connection therebetween.

If it is desired merely to clean the locking mechanism 40, it is not necessary to remove front sight 91]. rearwardly over the tube '20. Gas cylinder 599 is unscrewed from the threads on the barrel and moved forwardly. The retaining spring 493 is snapped out of engagement with piston plugs llil and then the piston plugs 450 may be withdrawn radially. The unlocking ring will then be free to be movedY forwardly of tube 22, thereby exposing all necessary surfaces for cleaning purposes. If it is desired to disassemble the barrel 35 and the operating spring 236i from tube 23, then the front sight Sil must be removed by unscrewing screw 92, whereupon the barrel may be withdrawn rearwardly out of tube 20. Spring retainer 293 is then rotated 90 degrees and Withdrawn through the slots 225 in tube 2li. The securing pin 22 in mounting ring is then knocked out and the mounting ring and spring 293 may then be slipped off of tube 2G.

An alternative form of locking mechanism le is disclosed in Figs. 6 and 7. This form will, for convenience, be hereafter referred to as the jet action lock. At the forward end of tube 2B in a thick Walled portion 2li) thereof, a" pair of opposed transverse slots 213 are provided which cut completely through a portion of the inner wall of tube 2li. Within each slot 213, a lockingshoe 215 is pivotally mounted on a pin 2id which extends generally parallel to the axis of tube 29. The inner surface 216 of shoes Handguard 3 may be withdrawn l2 215 is arcuately shaped to snugly t around cylindrical barrel portion 304.

An annular locking ring 356 of hardened steel is pressed onto barrel portion 3M and rests against a shoulder formed at the juncture of barrel portion 394 with larger diameter barrel portion 301. The external diameter of locking ring 396 is the same as that of barrel portion 391 and the length of locking ring 3116 is proportioned so that when its forward wall engages the shoes 215, the barrel is positioned in proper headspace relationship t0 breech block 10.

Locking shoes 215 are shaped in such manner that limited pivotal movement thereof will carry the shoes out of the path of locking ring 356 on the barrel. The external periphery 21'1 of shoes 215 is shaped to lie substantially flush with the periphery of the portion 219 of tube 20 when each shoe 215 is pivoted outwardly to its unlocked position. A recess 218 is centrally milled in, that portion of the shoe where the pin 214 passes through. A suitable torsion spring 219 is located in each recess 213, surrounding pin 214, and having one end 220 in engagement with the tube portion 219 and the other end 221 engaging its respective shoe 215. The springs 219 thus bias shoes 215 towards their locked position with respect to the barrel.

A gas baille 228 is provided comprising an annular ring surrounding the barrel immediately forward oflocking shoes 215. Baffie 229 engages the interior of tube 211 in bearing relation and prevents leakage of gas forwardly when shoes 215 are in their locked position. A pair of opposed longitudinal grooves 229 are provided in baille 228 to permit passage of the gas forwardly when the locking shoes are pivoted to their unlocked position. Y

With this arrangement the shoes 215 can be unlocked by the direct action of the barrel gases thereon. Gas ports 34 are provided in the barrel 39, opening respectively immediately beneath the arcuate surfaces 213 of locking shoes 215. The impact of the jet of gases passing through ports 34 has sufficient force to rotate each locking shoe 215 to its unlocked position. To facilitate the action of the gases on the shoes 215, a generally conical or arcuate recess 222 may be provided in the surface 216 of each shoe 215, immediately over-lying gas port 34. Y

After moving shoes 215 to an unlocked position, the gas then ows forwardly through grooves 229 into gas cylinder 558i'. Gas cylinder comprises an annular member having a large diameter rear portion 561 sliding in bearing relation on the forward end portion 219 of tube 2G and a small diameter forward portion 562 sliding in bearing relation on barrel portion 304. A barrel nut 565 is threadably secured to barrel portion 354 about a half-inch forwardly of the end of gas cylinder 565 so that gas cylinder 569 accelerates forwardly under the force of the gases and then picks up the barrely moving it forwardly, by impact with nut 565.

In order to permit the described jet action locking arrangement to be manually unlocked, annular cam surfaces 24B are provided on the exterior of each opposed end of the shoes 215. A cam extension 553 is integrally formed on the gas cylinder 569, comprising an arcuate cross-section, rearwardly extending projection. The interior surface 554 of extension 563 is shaped to denne a cam 556 which simultaneously engages cam surfaces 'Mil on shoes 215 as the 13 gas cylinder moves forward. The gas cylinder 560 is moved forward manually by the handguard or forearm 3 which comprises a hollow generally cylindrical member mounted in surrounding relation to the forward end of tube 20 and abutting a shoulder 561 on the periphery of gas cylinder 550. Thus as gas cylinder 560 is manually moved forward, the locking shoes 2I5 are cammed out of locking position by cam extension 563. At the completion of the cammed movement of shoes 2I5, gas cylinder 560 moves into engagement with barrel nut 565 and further forward movement of the gas cylinder moves the barrel forwardly to open the action. This movement brings the relatively larger diameter periphery ofY locking ring 306. and then barrel porhad the common characteristic of permitting the gas to operate directly upon the locking arrangement. lThis is, of course, advantageous from the standpoint of simplifying construction and reducing weight. With extremely high-powered cartridges, however, and where the overall length i of tube 20 is such that the gas port will be located close to the chamber end of the barrel, the modifications disclosed in Figs. 8, 11 and 21 may be more advantageous inasmuch as they provide a positive delay time before unlocking is n initiated,

Figs. 8 to 10 disclose a delay type locking mechanism 4l) which will hereafter be referred to as the roller type. A breech block (not shown), a tube 20 and barrel 30 are provided which are substantially identical to the construction heretofore described. The forward portion 224 of tube 20 is cf uniform interior diameter and has a thick walled portion 231 and a pair of diametrically opposed slots 225 are provided in such portion, the longitudinal axes of which are disposed in a plane substantially perpendicular to the axis of tube 2B.

A hardened locking ring 3I0 is provided surrounding barrel portion 3M and abutting the shoulder formed by the juncture with larger diameter barrel portion 33|. A pair of semi-cylindrical recesses 3I2 are provided in the rear portion of locking ring 3I3 respectively adjacent and parallel to slots 225 in tube 23. locking rollers 3I3 are provided comprising essentially cylindrical members which may move transversely through the slots 225 in tube 2) to snugly engage in the semi-cylindrical recesses SI2 in locking ring SIEL It will be apparent that when rollers 3I3 are retained in engagement in recesses 3I2 of locking ring 3H), the barrel will be rigidly locked to the tube 20 and hence be in safe condition for firing. Any forward force on the barrel, however, tends to cam the rollers 3I3 outwardly to an unlocked position.

The position of rollers 3I3 is respectively controlled by a pair of cam rods 3I4 which in turn are operated by a gas cylinder SIG. Gas cylinder 5I@ has a hollow cylindrical forward portion 5I I, constructed to slide in bearing relationship on barrel portion Bild. Rearwardly of bearing portion 5I I, the gas cylinder is of a larger diameter 5I2 and provided with a bore 5I3 permitting this portion of the gas cylinder 5H) to engage the A pair of I4 forward end portion 224 of the tube 20 in bearing relation. Cam rods 3| 4 are each suitably secured, as by pins 3II in rearwardly opening holes 5I$ provided in large diameter portion 5I2 of gas cylinder 5H). The center portion 3I5 of each roller 3I3 is of reduced diameter and the width of cam rods 3M is such as to permit the rods to freely engage center portion 3I5 of rollers 3I3. The surfaces of cam rods 3I respectively adjacent the rollers 3 I3 control the positioning of such rollers and hence control the locking and unlocking of the action. The locking portion 3I6 of cam rods 3M is located immediately adjacent gas cylinder 5I!) and extends rearwardly past rollers 3I3 for a distance proportional to the `amountn of pre-unlocking delay time desired.

Then an inclined cam surface 3I'I connects locking surface 3 I6 with an unlocking surface 3 I8 on each of cam rods 3I4. If no other means are provided to retain rollers 3I3 within tube 20, then it is necessary that the unlocking portion of cam rods 3M extend rearwardly a distance not less than the full stroke of the barrel 30. The ends of cam rods 3M may, therefore, be conveniently attached to the projections 204 provided on spring retainer 203. Hence operating spring 296 biases cam rods 314 and hence gas cylinder SIU rearwardly to their locked positions.

From the foregoing description it will be apparent that the initial forward movement of gas cylinder 5H! with respect to tube 20 produces no change in the locked relationship of the barrel and the tube until the gas cylinder has moved sufpiently forward to bring unlocking surface 3I8 of cam rod 3I4 past the locking rollers 3I3. Thus a time delay of any desired magnitude may be produced between the ring of the cartridge and the unlocking of the action by proper proportioning cf the length of the locking portion BIE and cam rods 3M. A barrel nut 320 is threadably secured to barrel 30 suiiciently forward of gas cylinder 5I() so that the gas cylinder will not contact nut 320 until locking rollers 3I3 are moved to their unlocked position. Thus gas cylinder 5I() will pick up barrel 30 by striking the nut 32H and move the barrel forwardly.

With such a locking arrangement it is desirable to utilize expansion of the gases as the primary actuating force, inasmuch as the relatively long delay in unlocking may result in insufficient gas pressure within the barrel to drive the gas cylinder and barrel forwardly after unlocking. Such gas expansion feature may be conveniently applied to the described construction by providing a counterbore Sie in the intermediate portion of the rear large diameter section SI2 of the gas cylinder 5H). A gas port 3S may then be provided in barrel 30 and locking ring SIU which in the battery position of the barrel is disposed forwardly of the rear shoulder SI5 formed in gas cylinder 5I0 at the juncture of bore 5I3 with the counterbore 5I4. A suitable radial passage 226 is provided in tube 20 in alignment with gas port 3B.

With this arrangement a portion of the gases developed in the barrel will enter the gas cylinder Ei through gas port 36 and will operate on gas cylinder 5I0 to drive it forwardly. However, after limited forward movement of gas cylinder 55e, and before the pressure within the barrel 39 has decreased substantially, the shoulder 5I5 of the gas cylinder will override the gas passage 226 in tube 20, thereby effectively providing a sealed-off gas chamber within the gas cylinder 5H). Thus the gases will continue to operate by expansion to accelerate the gas cylinder 5H) forwardly, thereby unlocking locking rollers 3 i3 and picking up the barrel by collision with barrel nut 32S. Just beyond this point the rear end oi gas cylinder i will pass olf the forward end of tube 2@ and exhaust the residual gases. The barrel, however, has received sufficient acceleration to carry it to its eXtreme forward position as illustrated in Fig. 9, compressing operating spring 206.

On the return stroke operating spring 206 functions on barrel 3G through the engagement of gas cylinder El@ with the forward end of locking ring 31S. The cam surfaces 3 l1 on cam rods 3H! will therefore strike the rollers M3 prior to the barrel reaching its battery position.V While this interrupts the spring action of operating spring 296 upon the barrel, the barrel, due to its large mass, has more than sufficient momentum to permit it to coast into its battery position. Hence a spring bias will be maintained on the rollers 313 which will snap them into locked position in the recesses 312 when the barrel coasts into its battery position.

Quantity production modelsgas operated, positice lock, automatic rifles Referring to Figs. ll through 25, there will now be described modifications of this invention com prising gas operated, positive lock, automatic nrearms which have been designed in such manner as to be readily adaptable to quantity production, inasmuch as all of the major elements of the riiie are either cylindrical components or stampings.

As in the previous constructions, a breech block 1Z0 (Figs. 1l and i3) threadably secured to the rear end or" a hollow tube 2li and a barrel 3! reciprocates within tube 2t. The r-ear portion of tube 25E is identical to that previously described. being provided with magazine slot 2l and cartridge ejection slot E3 (Fig. 14). The breech block 12e, however, has been substantially modified to make it more readily manufacturable. Breech block lft now comprises a cylindrical member having an axial threaded recess li (Figs. il and 13) in its forward end to accommodate the threaded rear end of tube Eil. The cooperating threads between recess l2! and tube 2:2 are preferably of the interrupted type, permitting full engagement of the threads by limited rotation of the tube 2t relative to the breech block las. In the center of the base of recess 25, a cylindrical cartridge seating recess 522 is provided. An axial firing pin opening IZS (Figs. ll and 17) is provided through breech block lll, having an enlarged, rearwardly opening, counterbored portion iid which accommodates the enlarged head E26 of a iiring pin E25. A ring pin spring l2? operates between the head H26 of the ring pin and the base of the counterbore E26. Firing pin i253 is retained in breech block I2@ by means of a washer M3 (Fig. 17) which is secured by a bolt il@ in a recess l le on the rear face of breech block E25. Washer H3 engages a rearwardly facing shoulder H9 formed by milling a longitudinal flat on the head portion E26 of firing pin lili.

A magazine support lli@ (Figs, l1, l2, and 14) is provided which may be conveniently formed by stamping of sheet metal. Magazine support 55 is preferably formed in two halves divided by a plane passed vertically through the barrel axis of the rearm and then the two half portions are welded together. The magazine supn port includes a rear cylindrical portion l5! conv structed to fit snugly around breech block IZS.

Magazine sup-port 158 has also a forward cylindrical portion 52 which is constructed to snugly engage the periphery of tube 2t. The central portion l3 (Fig. 13) oi the magazine support comprising spaced, longitudinally extending walls is shaped to denne a magazine recess into which a magazine itil may be snugly inserted. On each side of the central portion it, there are respectively provided a forward web portion S55 and a rear web portion [5S (Fig. l1). The two half sections from which the magazine support Lit is formed may be conveniently secured together by spot welding in the forward web portion and by welding the two halves of the rear web portion 56 to a spacer block lill thus deiining a channel 153 (Fig. le). A magazine latch it may be conveniently mounted in the channel |53 by means of a pin itil passing through a suitable hole in the magazine latch i519.

The rear cylindrical portion lill of magazine support 56 is suitably secured as, for example, by spot welding to the breech block Vit. A pair of spaced vertical ears H55 l1) are formed from the rear cylindrical portion 55 projecting above the breech block 2li to form a bracket for mounting a rear sight lil'. Likewise a pair of spaced upstanding ears Hi8 (Fig. 14) are formed from the forward cylindrical portion E52 of magazine support l5!! to provide a mounting bracket for a lcartridge locator t9 that is fully described in my copending application for Firing Mechanism for Automatic Firearms, Serial No, 59,324, iiled November l0, i948. The magazine it@ when latched in position in the magazine recess projects upwardly into a correspondingly shaped opening 2l (Fig. 14) provided in the tube 20.

Up to this point the barrel St has been described as an integral member similar to the construction shown in previously described modifloat-ions and obviously the locking and gas systems already described may be utilized. The previously described modications all utilized a relatively small gas cylinder to move the barrel forwardly and the total weight of such gas cylinder was only a small fraction of the weight of the barrel. This construction, therefore, requires that considerable gas be admitted t0 the cylinder and permitted to operate upon the cylinder after the cylinder had picked up the barrel in order that sufficient energy could be imparted to the barrel to move it to its extreme forward position. It would be obviously desirable to provide a construction wherein the weight of the gas cylinder was a substantial proportion of the weight of the barrel. Such objective has been accomplished in the modied form of barrel and locking mechanism now tc be described, without increasing the overall weight of the gun or decreasing the effective weight of the barrel.

As shown in Figs. ll and 13, the barrel may be said to be formed in two pieces, comprising a relatively thin-walled barrel portion which includes the chamber 325 and. a. rifled bore 32?, and a barrel operating sleeve 328 which slidably surrounds the rear portion of the barrel element 325, running from a point approximately one-half inch forwardly of the chamber and to at least a point beyond the forward end of the tube 20. The total mass of the barrel element 325 and barrel sleeve 328 is selected to be not less than the mass of the integral barrel utilized in the previous modifications, It is apparent, therefore, that so far as rigidity of the barrel for bayonet work, heat resistancev oi the barrel under contmued ring, and the cyclic rate of automatic fire of the weapon are concerned, this two-plete barrel construction will .function equally as woll as the previously described integral oonstruotion- As a matter of fact the cooling rate of such barrel will be somewhat greater inasmuch as relative movement (which will be described) between the sleeve 328 and the barrel element 325 permits exposure of a hotter portion of the barrel for eiroooline. yet does not impair the loes of heat from the barrel by conduction.

Barrel element 325 is formed with essentially three distinct diameters, the largest diameter portion 329 comprises the extreme rear` end of the barrel element .3.25 and is of such diameter 3S. t0 permit large diameter portion `323 to cooperate in bearing relationship with the uniform diameter bore 236 o f the tube 23. This large diameter portion 323 is of limited length, being just lone enough to accommodate the threaded hole in which the cooking rod Bull secured into the barrel. Next, an intermediate diameter por.- tion 33|! is provided which preferably extends forwardly to a point beyond the forward end of the magazine opening 2| in tube .20. Finally, the remainder of the forward portion of the barrel element 32,5 is preferably of substantially uniform `small diameter 33|. A substantial ,Sized forwardly facing shoulder .332 is thereby formed et the iunoture of diameter portions 33o and 33| which will be utilized es e ,locking shoulder for rthe barrel. It 'is desired to point out that while shoulder 332 is preferably located to lie forwardly of the maga-zine opening in the tube when the barrel is in its battery position, in some applications of this invention 4it may be desirable to move such shoulder back further alone the barrel, This, of course, has the eect of moving the point of locking of the action closer to vthe face of the breech member.

The barrel sleeve 328 has a uniform exterior fr diameter 333 which cooperates in bearing rela tionship with the uniform diameter bore 23D of the tube 20,. The bore of Sleeve 328 Ais formed in two diameters, a rearward large diameter pore tions 3.34 which cooperates with the intermediate portion of the barrel element 325 and a forward smaller diameter portion 335 (Fig. 1l) which cooperates in bearing relationship with the smell diameter portion 33| of the Abarrel element l32,5.

The extreme forward end o f `barrel sleeve 328 Ais provided with threads 336 which yproject beyond `the end of tube 20. An annular gas cylinder .5,23 is provided with a forward threaded portion 5|'l which engages the thread 336 on barrel sleeve 328 and a rearwardly extending cylinder portion 5|8 which cooperates in bearing relationship with a bushing 23| which is secured by a key 363 to the forward end of tube 20. Thus in effect the gas cylinder is supplied with a mass that is a substantial proportion of the mass of the barrel element `325.

The barrel velement 325 is locked to the tube 2.0 by means of a locking element 3.40. Locking element 34|] has an annular base portion 34| (Fig. 18) which fits freely over the small diameter portion 33| of barrel element 325 and within the rear large diameter portion 334 Iof the sleeve 323 (Fig, 19j). Two diametrically opposed locking projections 342 are integrally provided on the annular portion 34| projecting outwardly through cam `slots 343 in barrel sleeve 328 (Figs. 11, 13, 15, 18 and 19) and into locking slots 232 in tube 23. Locking slots 232 (Fig. '15) have parallel portions 233 extending forwardly along tube 23 for a distance greater than the desired QIWfId. movement of the barrel element 325 and terminating in wider assembly slots 235. The rear end of looking slots 232 are provided with helical locking portions 2 34 which are peripherally offset with respect to the parallel portion 233 thus dening rearwardly facing locking surfaces 236.

The locking projections 342 are each provided with a helical locking surface 334 (Fig. 18) which are brought into engagement with the corresponding'lccking surface 236 of locking slots 232 by rotation of the locking element 340 with respoot to the barrel element 325. The cam slots 323 in barrel sleeve 328 accomplish the rotation of the locking element between its locked and unlocked positions by engagement with camming surfaces V333 (Fig. 18) provided on the locking projections 362 of the locking element 340. Cam slots 333 are shaped to denne a forward wide assembly portion 33? (Fig. il), and a straight, narrow rearwardly extending dwell travel portion 345 which terminates in a helical cam portion 346. Barrel sleeve 325 is biased against rotation by key 333 (Fig. 1l) inserted through the wall of tube 2i) and bushing 23| and engaging in a longitudinal key slot 362 provided in barrel sleeve 328. Thus the barrel sleeve 328 must be rst moved forwardly with respect to barrel element 325 by gas cylinder 52|] for a distance determined by the length of dwell travel portions 3.45 of cam Yslots 3.43. Then the continued forward movement of barrel sleeve 328 will rotate locking elements 320 by engagement of the helical cam portions 343 in the sleeve with correspondingly shaped cam portions (not shown) provided on the locking element 340. Further forward movement of barrel sleeve 328 brings its front end into engagement with a barrel nui-I 360 (Fig. 12) threadably secured to barrel element 325. Thus the barrel element 32.5 is picked up and carried to its extreme forward position by the barrel sleeve 328. The locking projections 342 are made sufficiently long so as to project out of the tube 2|) and the projecting ends thereof may thus be utilized as a seat for the operating spring 296. Operating spring 206 is thus compressed by forward movement of barrel element y325. The front end turn of spring 236 seats in a Aslot 364 in key 363, thus retaining the key in position. To cushion the impact between barrel sleeve 328 and nut 365), a Vspring 36| may be provided operating therebetween. Spring 36| also assists in returning sleeve 328 to its battery position after barrel element 325 is locked. In addition, a buffer ring (not shown) of fibrous or plastic material may be mounted between barrel sleeve 328 and barrel nut 360 to cushion the impact.

The return movement of barrel element 325 and sleeve 328 is produced by operating spring 206. When the locking projections 34.2 reach the end .of the parallel slot portions 233 in tube 20, initiation of rotation of locking element 34o is produced by the radius 233e joining slot portions 233 with helical locking slots 234. The completion .of rotation of locking element 34o is then accomplished by the helical cam slot portions 343 in sleeve 328.

Assembly of tube 2|), barrel 325, barrel sleeve 328, and locking element 3,40 is accomplished prior to screwing breech block |20 into tube 2|). Barrel sleeve 328 is inserted in tube 20 and assembiy slot portions 235 of the tube are aligned with assembly slot portions 331 of the sleeve. Locking element 340 is then turned 9.0 degrees 

